Mobile communication method and radio terminal

ABSTRACT

A mobile communication method, which configures a DRX cycle having an On duration in which a downlink signal transmitted from a serving base station is to be monitored and an Off duration other than the On duration in an RRC connected state where an RRC connection is established between a radio terminal and a radio base station, the mobile communication method comprising: a step A of transmitting, from the radio terminal to the radio base station, a timing adjustment request uplink signal through an uplink control channel, even when a radio resource of an uplink data channel has not been assigned in a case where the DRX cycle is configured; and a step B of transmitting, from the radio base station to the radio terminal, transmission timing correction information of an uplink signal, in response to the timing adjustment request uplink signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication method, whichconfigures a DRX cycle (a discontinuous reception cycle) having an Onduration, in which a downlink signal transmitted from a serving cell isto be monitored, and an Off duration other than the On duration, and aradio terminal.

2. Description of the Related Art

In the next generation communication system such as LTE (Long TermEvolution), in order to reduce the power consumption of a radioterminal, a technology called DRX (Discontinuous Reception) is employed(for example, TS36.321 V10.0.0).

In the DRX, a DRX cycle has an On duration, in which a downlink signal(for example, PDCCH: Physical Downlink Control Channel) transmitted froma serving cell is to be monitored, and an Off duration (Opportunity forDRX) other than the On duration. A radio base station transmits adedicated signal addressed to a radio terminal only in an On duration ofthe radio terminal. As described above, the configuration is such thatthe radio terminal may monitor the downlink signal transmitted from theradio base station, only in the On duration, and may turn off its ownreceiver in the Off duration. In addition, the DRX cycle may include twocycles (a short DRX cycle and a long DRX cycle). Furthermore, a DRX modemay be configured in the state in which an RRC connection is establishedbetween the radio terminal and the radio base station (RRC connectedstate). That is, it should be noted that the Off duration of the DRXcycle is different from an RRC idle state. In addition, in the 3GPPstandard, the long DRX cycle is mandatory and the short DRX cycle isoptional.

However, in recent years, there have been increased radio terminalshaving various applications. The application is configured toperiodically transmit and receive a predetermined message such as akeep-alive message or a state update message to/from a communicationcorrespondent such as a server. In such a case, since a control signalis transmitted and received due to the transition toward an RRC state,whenever the predetermined message is transmitted or received, ashortage of a network resource will be caused.

In this regard, in order to suppress the shortage of the networkresource, the provision of a DRX cycle (for example, an extended DRXcycle) longer than the existing DRX cycle (for example, the short DRXcycle and the long DRX cycle) (for example, RP-110454) is underconsideration.

However, it is assumed that the length of the extended DRX cycle isseveral seconds or more and the extended DRX cycle is very long ascompared with the short DRX cycle, the long DRX cycle and the like.Therefore, the Off duration of the extended DRX cycle is expected to bevery long.

Therefore, when the extended DRX cycle is configured, variouscountermeasures are considered necessary. For example, in a process ofaligning the timing at which a radio base station receives an uplinksignal from a radio terminal, it is necessary for the radio terminal toreceive transmission timing correction information (hereinafter,referred to as TA; Timing Advance) of the uplink signal. However, sincethe radio terminal receives the TA only in an On duration, an intervalfor receiving the transmission timing correction information (TA) mayexceed an interval (hereinafter, referred to as a maximum TA receptioninterval) in which the TA is to be received. In such a case, a shift ofsynchronization in an uplink from the radio terminal may be caused.

SUMMARY OF THE INVENTION

A mobile communication method of a first feature configures a DRX cyclehaving an On duration in which a downlink signal transmitted from aserving base station is to be monitored and an Off duration other thanthe On duration in an RRC connected state where an RRC connection isestablished between a radio terminal and a radio base station. Themobile communication method comprises: a step A of transmitting, fromthe radio terminal to the radio base station, a timing adjustmentrequest uplink signal through an uplink control channel, even when aradio resource of an uplink data channel has not been assigned in a casewhere the DRX cycle is configured; and a step B of transmitting, fromthe radio base station to the radio terminal, transmission timingcorrection information (TA) of an uplink signal, in response to thetiming adjustment request uplink signal.

In the first feature, the step A comprises: a step of transmitting, fromthe radio terminal to the radio base station, the timing adjustmentrequest uplink signal, when a movement speed of the radio terminalexceeds a predetermined threshold value.

In the first feature, the mobile communication method comprises: a stepC of deciding, at the radio base station, a maximum reception interval,in which the transmission timing correction information (TA) is to bereceived, based on a movement speed of the radio terminal; and a step Dof transmitting, from the radio base station to the radio terminal, themaximum reception interval.

In the first feature, the step A comprises: a step of transmitting, fromthe radio terminal to the radio base station, the timing adjustmentrequest uplink signal, before a reception interval of the transmissiontiming correction information (TA) exceeds the maximum receptioninterval.

A radio terminal of a second feature is configured to receive a downlinksignal in a mobile communication system, which configures a DRX cyclehaving an On duration in which the downlink signal transmitted from aserving base station is to be monitored and an Off duration other thanthe On duration in an RRC connected state where an RRC connection isestablished between the radio terminal and a radio base station. Theradio terminal comprises: a control unit configured to transmit a timingadjustment request uplink signal to the radio base station through anuplink control channel, even when a radio resource of an uplink datachannel has not been assigned in a case where the DRX cycle isconfigured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a mobile communication system 100according to a first embodiment.

FIG. 2 is a diagram illustrating a radio frame according to the firstembodiment.

FIG. 3 is a diagram illustrating a radio resource according to the firstembodiment.

FIG. 4 is a diagram illustrating a short DRX cycle according to thefirst embodiment.

FIG. 5 is a diagram illustrating a long DRX cycle according to the firstembodiment.

FIG. 6 is a diagram illustrating an extended DRX cycle according to thefirst embodiment.

FIG. 7 is a block diagram illustrating UE 10 according to the firstembodiment.

FIG. 8 is a sequence diagram illustrating a mobile communication methodaccording to the first embodiment.

FIG. 9 is a sequence diagram illustrating a mobile communication methodaccording to the first modification.

FIG. 10 is a sequence diagram illustrating a mobile communication methodaccording to the second modification.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A mobile communication system according to an embodiment of the presentinvention is described below with reference to the drawings. Note that,in the following description of the drawings, same or similar referencesigns denote same or similar elements and portions.

In addition, it should be noted that the drawings are schematic andratios of dimensions and the like are different from actual ones.Therefore, specific dimensions and the like should be determined inconsideration of the following description. Moreover, the drawings alsoinclude portions having different dimensional relationships and ratiosfrom each other.

Overview of Embodiment

A mobile communication method of an embodiment configures a DRX cyclehaving an On duration in which a downlink signal transmitted from aserving base station is to be monitored and an Off duration other thanthe On duration in an RRC connected state where an RRC connection isestablished between a radio terminal and a radio base station. Themobile communication method comprises: a step A of transmitting, fromthe radio terminal to the radio base station, a timing adjustmentrequest uplink signal through an uplink control channel, even when aradio resource of an uplink data channel has not been assigned in a casewhere the DRX cycle is configured; and a step B of transmitting, fromthe radio base station to the radio terminal, transmission timingcorrection information (TA) of an uplink signal, in response to thetiming adjustment request uplink signal.

According to an embodiment, the radio terminal transmits a timingadjustment request uplink signal, even when a radio resource of anuplink data channel is not assigned in the case where a DRX cycle isconfigured. Consequently, even when a very long DRX cycle is configured,since transmission timing correction information (TA) is transmittedfrom a radio base station, a shift of synchronization between the radioterminal and the radio base station is suppressed.

According to the embodiment, the radio terminal transmits the timingadjustment request uplink signal through an uplink control channel, inthe case where the DRX cycle is configured. Consequently, the shift ofthe synchronization between the radio terminal and the radio basestation is suppressed without releasing the DRX cycle.

First Embodiment (Mobile Communication System)

Hereinafter, a mobile communication system according to a firstembodiment will be described. FIG. 1 is a diagram illustrating themobile communication system 100 according to a first embodiment.

As illustrated in FIG. 1, the mobile communication system 100 includes aradio terminal 10 (hereinafter, referred to as UE 10) and a core network50. Furthermore, the mobile communication system 100 includes a firstcommunication system and a second communication system.

The first communication system, for example, is an LTE (Long TermEvolution)-compatible communication system. The first communicationsystem, for example, includes a radio base station 110 (hereinafter,referred to as eNB 110) and MME 120. In addition, in the firstcommunication system, a first RAT (EUTRAN; Evolved Universal TerrestrialAccess Network) is used.

The second communication system, for example, is a WCDMA (Wideband CodeDivision Multiple Access)-compatible communication system. The secondcommunication system, for example, includes a radio base station 210,RNC 220, and SGSN 230. In addition, in the second communication system,a second RAT (UTRAN; Universal Terrestrial Access Network) is used.

The UE 10 is a device (User Equipment) configured to communicate withthe first communication system and the second communication system. Forexample, the UE 10 has a function of performing radio communication withthe eNB 110, and a function of performing radio communication with theradio base station 210.

The eNB 110, having a cell 111, is a device (evolved NodeB) configuredto perform radio communication with the UE 10 existing in the cell 111.

The MME 120 is a device (Mobility Management Entity) configured tomanage the mobility of the UE 10 which establishes a radio connectionwith the eNB 110. The MME 120 is provided in the core network 50.

The radio base station 210, having a cell 211, is a device (NodeB)configured to perform radio communication with the UE 10 existing in thecell 211.

The RNC 220, connected to the radio base station 210, is a device (RadioNetwork Controller) configured to establish a radio connection (RRCConnection) with the UE 10 existing in the cell 211.

The SGSN 230 is a device (Serving GPRS Support Node) configured toperform packet switching in a packet switching domain. The SGSN 230 isprovided in the core network 50. Although not illustrated in FIG. 1, adevice (MSC; Mobile Switching Center) configured to perform circuitswitching in a circuit switching domain may be provided in the corenetwork 50.

Hereinafter, the first communication system will be mainly described.The following description may also be applied to the secondcommunication system. Furthermore, a cell should be understood as afunction of performing radio communication with the UE 10. The cell mayalso be considered as a service area indicating a range communicablewith the cell.

Here, in the first communication system, an OFDMA (Orthogonal FrequencyDivision Multiple Access) scheme is used as a downlink multiplexingscheme, and an SC-FDMA (Single-Carrier Frequency Division MultipleAccess) scheme is used as an uplink multiplexing scheme.

Furthermore, in the first communication system, an uplink channelincludes an uplink control channel (PUCCH; Physical Uplink ControlChannel), an uplink shared channel (PUSCH; Physical Uplink SharedChannel), and the like. Furthermore, a downlink channel includes adownlink control channel (PDCCH; Physical Downlink Control Channel), adownlink shared channel (PDSCH; Physical Downlink Shared Channel), andthe like.

The uplink control channel is used to transfer a control signal. Thecontrol signal, for example, includes CQI (Channel Quality Indictor),PMI (Precoding Matrix Indicator), RI (Rank Indicator), SR (SchedulingRequest), and ACK/NACK.

The CQI is a signal for notifying a recommended modulation scheme and acoding rate to be used in downlink transmission. The PMI is a signalindicating a precoder matrix which is preferably used in downlinktransmission. The RI is a signal indicating the number of layers(streams) to be used in downlink transmission. The SR is a signal forrequesting the assignment of an uplink radio resource (a resource blockwhich will be described later). The ACK/NACK is a signal indicatingwhether a signal transmitted through the downlink channel (for example,the PDSCH) has been successfully received.

The uplink shared channel is used to transfer a control signal (includesthe above-mentioned control signal) and/or a data signal. For example,the uplink radio resource may be assigned only to the data signal, orassigned such that the data signal and the control signal aremultiplexed.

The downlink control channel is used to transfer a control signal. Thecontrol signal, for example, includes Uplink SI (SchedulingInformation), Downlink SI (Scheduling Information), and a TPC bit.

The Uplink SI is a signal indicating the assignment of the uplink radioresource. The Downlink SI is a signal indicating the assignment of adownlink radio resource. The TPC bit is a signal for instructingincrease or decrease in the power of a signal transmitted through theuplink channel.

The downlink shared channel is used to transfer a control signal and/ora data signal. For example, the downlink radio resource may be assignedonly to the data signal, or assigned such that the data signal and thecontrol signal are multiplexed.

In addition, a control signal transmitted through the downlink sharedchannel includes TA (Timing Advance). The TA is transmission timingcorrection information between the UE 10 and the eNB 110, and ismeasured by the eNB 110 based on an uplink signal transmitted from theUE 10.

Furthermore, a control signal transmitted through a channel, other thanthe downlink control channel (the PDCCH) and the downlink shared channel(the PDSCH), includes ACK/NACK. The ACK/NACK is a signal indicatingwhether a signal transmitted through the uplink channel (for example,the PUSCH) has been successfully received.

(Radio Frame)

Hereinafter, a radio frame in the first communication system will bedescribed. FIG. 2 is a diagram illustrating the radio frame in the firstcommunication system.

As illustrated in FIG. 2, one radio frame includes 10 subframes and onesubframe includes two slots. One slot has a time length of 0.5 msec, onesubframe has a time length of 1 msec, and one radio frame has a timelength of 10 msec.

In addition, one slot includes a plurality of OFDM symbols (for example,six OFDM symbols or seven OFDM symbols) in the downward direction. Inthe same manner, one slot includes a plurality of SC-FDMA symbols (forexample, six SC-FDMA symbols or seven SC-FDMA symbols) in the upwarddirection.

(Radio Resource)

Hereinafter, a radio resource in the first communication system will bedescribed. FIG. 3 is a diagram illustrating the radio resource in thefirst communication system.

As illustrated in FIG. 3, a radio resource is defined by a frequencyaxis and a time axis. A frequency includes a plurality of subcarriers,and a predetermined number of subcarriers (12 subcarriers) arecollectively called a resource block (RB). A time has a unit, such asthe OFDM symbol (or the SC-FDMA symbol), the slot, the subframe, or theradio frame, as described above.

Here, the radio resource is assignable to each resource block.Furthermore, on the frequency axis and the time axis, it is possible todivide the radio resources to assign the same to a plurality of users(for example, user #1 to user #5).

Furthermore, the radio resource is assigned by the eNB 110. The eNB 110assigns the radio resource to each UE 10 based on the CQI, the PMI, theRI and the like.

(Discontinuous Reception)

Hereinafter, a discontinuous reception (DRX) will be described. FIG. 4to FIG. 6 are diagrams explaining the discontinuous reception. In orderto reduce power consumption, it is possible for the UE 10 to configurethe discontinuous reception. Hereinafter, a description will be providedfor the case where the discontinuous reception is configured in thestate in which an RRC connection is established between the UE 10 andthe eNB 110 (an RRC connected state).

As illustrated in FIG. 4 to FIG. 6, according to the discontinuousreception (DRX), a DRX cycle has an On duration, in which a downlinksignal transmitted from a serving cell is to be monitored, and an Offduration (Opportunity for DRX) other than the On duration. The eNB 110transmits a dedicated signal addressed to the UE 10 only in an Onduration of the UE 10. As described above, the configuration is suchthat it suffices to monitor the downlink signal (for example, the PDCCH:Physical Downlink Control Channel), which is transmitted from the eNB110, only in the On duration, and probably, the UE 10 turns off its ownreceiver in the Off duration.

In addition, the DRX cycle may include a plurality of types of cycles.Hereinafter, three DRX cycles (a short DRX cycle, a long DRX cycle, andan extended DRX cycle) will be described.

As illustrated in FIG. 4, the short DRX cycle is a short cycle. Thelength of the short DRX cycle is not particularly limited, and is theorder of several milliseconds (for example, 80 msec).

For example, the short DRX cycle is configured according to a command(DRX command) received from the eNB 110. Alternatively, the short DRXcycle is configured when a predetermined period has elapsed after thedownlink signal (for example, the PDCCH) is finally received. Inaddition, since the short DRX cycle is optional, it may not beconfigured.

As illustrated in FIG. 5, the long DRX cycle is longer than the shortDRX cycle. The length of the long DRX cycle is not particularly limited,and is the order of several milliseconds (for example, 160 msec).

For example, when the long DRX cycle is configured, a configurationparameter (DRX Config.) is notified from the eNB 110. The long DRX cycleis configured when a predetermined period has elapsed after the downlinksignal (for example, the PDCCH) is finally received. Alternatively, thelong DRX cycle is configured when a predetermined period has elapsedafter the short DRX cycle is configured.

As illustrated in FIG. 6, the extended DRX cycle is longer than the longDRX cycle. The length of the extended DRX cycle is not particularlylimited, and is very longer than the short DRX cycle and the long DRXcycle. For example, the extended DRX cycle is the order of severalseconds. For example, the extended DRX cycle is equivalent to a cycle (aPaging Channel Monitoring Cycle), in which a paging signal for notifyingthat the UE 10 receives an incoming call is monitored, in the state inwhich the RRC connection has not been established between the UE 10 andthe eNB 110 (an RRC idle state). Alternatively, in the RRC idle state,the extended DRX cycle is longer than a cycle in which the paging signalfor notifying that the UE 10 receives an incoming call is monitored.

For example, when the extended DRX cycle is configured, a configurationparameter (DRX Config.) is notified from the eNB 110. The extended DRXcycle is configured with the permission of the eNB 110 for a requestfrom the UE 10. Alternatively, the extended DRX cycle is configured whena predetermined period has elapsed after the downlink signal (forexample, the PDCCH) is finally received. Alternatively, the extended DRXcycle is configured when a predetermined period has elapsed after theshort DRX cycle or the long DRX cycle is configured. Furthermore, inother examples, the UE 10 may recognize a static configuration parameterin advance, and the extended DRX cycle may also be configured with thepermission of the eNB 110 for a request from the UE 10.

In addition, with an increase in the number of UEs 10 having variousapplications, the transition of an RRC state is increased due to anincrease in the transmission/reception of a predetermined message.Therefore, since it is estimated that a shortage of a radio resourcesuch as RACH (Random Access Channel) may be caused, the extended DRXcycle is configured in order to suppress the frequent transition of theRRC state in the UE 10 and to suppress the shortage of the networkresource. In addition, the predetermined message includes a message,such as a keep-alive message or a state update message, which istransmitted to a communication correspondent from various applicationsprovided in the UE 10.

(Radio Terminal)

Hereinafter, a radio terminal in the first embodiment will be described.FIG. 7 is a block diagram illustrating the UE 10 according to the firstembodiment. As illustrated in FIG. 7, the UE 10 includes a communicationunit 11 and a control unit 12.

The communication unit 11 receives a signal from the eNB 110 (or theradio base station 210). Alternatively, the communication unit 11transmits a signal to the eNB 110 (or the radio base station 210). Inaddition, the communication unit 11, for example, has an antenna (aplurality of antennas when MIMO is used), a demodulation unit, and amodulation unit.

The control unit 12 controls the UE 10. For example, when thediscontinuous reception (DRX) is configured, the control unit 12controls the on/off of the communication unit 11. That is, in the Onduration in which the downlink signal transmitted from the serving cellis to be monitored, the control unit 12 turns on the communication unit11 and monitors the downlink signal (for example, the PDCCH) transmittedfrom the eNB 110. In the Off duration other than the On duration inwhich the downlink signal transmitted from the serving cell is to bemonitored, the control unit 12 turns off the communication unit 11 anddoes not monitor the downlink signal (for example, the PDCCH)transmitted from the eNB 110.

Specifically, in the case where the DRX cycle is configured, even when aradio resource of the uplink data channel (for example, the PDSCH) hasnot been assigned, the control unit 12 transmits a timing adjustmentrequest uplink signal to the eNB 110 through the uplink control channel(for example, the PDCCH).

Here, the timing adjustment request uplink signal may be a pseudo signal(random information, zero information) which is added to the existingcontrol signal (for example, the CQI, the PMI, the RI, and the SRS).Alternatively, the timing adjustment request uplink signal may be apseudo signal (random information, zero information) which is newlydefined.

Furthermore, the timing adjustment request uplink signal is used whenthe eNB 110 measures a propagation delay time between the UE 10 and theeNB 110. In other words, the timing adjustment request uplink signal isa signal requesting the eNB 110 to transmit transmission timingcorrection information (TA; Timing Advance).

If the transmission timing correction information (TA) is received fromthe eNB 110, the control unit 12 adjusts a transmission timing of anuplink signal. The transmission timing, for example, is adjusted withthe accuracy of 16×Ts (0.52 μseconds). In addition, the Ts is a basicunit time in the LTE, and for example, 1/(15000×2048) second.

Here, it should be noted to determine a maximum TA reception interval inwhich the transmission timing correction information (TA) is to bereceived. For example, the maximum TA reception interval may be decidedby the eNB 110, and transmitted from the eNB 110 to the UE 10.Alternatively, the maximum TA reception interval may be decided by theUE 10. For example, the maximum TA reception interval is decided basedon the movement speed of the UE 10. Specifically, as the movement speedof the UE 10 is slower, a longer time is decided as the maximum TAreception interval.

Here, the control unit 12 has a predetermined timer(TimingAlignmentTimer) for monitoring an interval in which thetransmission timing correction information (TA) is received. If thetransmission timing correction information (TA) is received, the controlunit 12 sets the maximum TA reception interval to the predeterminedtimer. Thus, when the timer set with the maximum TA reception intervalhas expired, the control unit 12 determines that a shift ofsynchronization between the UE 10 and the eNB 110 is caused. In otherwords, if an interval of the transmission timing correction information(TA) continuously received from the eNB 110 exceeds the maximum TAreception interval, the control unit 12 determines that the shift of thesynchronization between the UE 10 and the eNB 110 is caused.

Here, before the predetermined timer with the set maximum TA receptioninterval is expired, it is preferable that the control unit 12 transmitsthe timing adjustment request uplink signal to the eNB 110.

In addition, the control unit 12 may transmit the timing adjustmentrequest uplink signal to the eNB 110 in a predetermined cycle.Alternatively, when the movement speed of the UE 10 exceeds apredetermined threshold value, the control unit 12 may transmit thetiming adjustment request uplink signal to the eNB 110.

In addition, the movement speed of the UE 10 may be measured by thenumber of handovers in a predetermined time. Alternatively, when the UE10 has GPS (Global Positioning System), the movement speed of the UE 10may be measured using the GPS. Alternatively, when the UE 10 has anacceleration sensor, the movement speed of the UE 10 may also bemeasured using the acceleration sensor.

(Mobile Communication Method)

Hereinafter, a mobile communication method in the first embodiment willbe described. FIG. 8 is a sequence diagram illustrating the mobilecommunication method according to the first embodiment.

As illustrated in FIG. 8, in step 10, the UE 10 transmits a connectionrequest (RRC Connection Request) to the eNB 110.

In step 20, the eNB 110 transmits a connection setup (RRC ConnectionSetup) to the UE 10.

In step 30, the UE 10 transmits a connection complete (RRC ConnectionComplete) to the eNB 110.

In step 40, the UE 10 configures DRX. For example, the UE 10 configuresan extended DRX cycle.

In step 50, the UE 10 transmits the timing adjustment request uplinksignal to the eNB 110 through the uplink control channel (for example,the PUSCH) even when a radio resource of the uplink data channel (forexample, the PUSCH) has not been assigned. Here, as an example, adescription will be provided for the case where the timing adjustmentrequest uplink signal is transmitted to the eNB 110 in a duration (thatis, the Off duration) other than the On duration, in which the downlinksignal transmitted from the serving cell is to be monitored.

In addition, the UE 10 may transmit the timing adjustment request uplinksignal to the eNB 110 in a predetermined cycle. Alternatively, when themovement speed of the UE 10 exceeds a predetermined threshold value, theUE 10 may also transmit the timing adjustment request uplink signal tothe eNB 110.

In step 60, the eNB 110 decides transmission timing correctioninformation (that is, the TA; Timing Advance) between the UE 10 and theeNB 110 according to the reception timing of the timing adjustmentrequest uplink signal.

In step 70, the eNB 110 transmits the transmission timing correctioninformation (TA) decided in step 60 to the UE 10. In addition, since theDRX is configured, it is preferable that the eNB 110 transmits thetransmission timing correction information (TA) in the On duration.

In step 80, the UE 10 adjusts the transmission timing of an uplinksignal based on the transmission timing correction information (TA)received from the eNB 110. In addition, the transmission timing, forexample, is adjusted with the accuracy of 16×Ts (0.52 mseconds) asdescribed above.

(Operation and Effect)

According to the first embodiment, in the case where the DRX cycle isconfigured, even when the radio resource of the uplink data channel hasnot been assigned, the UE 10 transmits the timing adjustment requestuplink signal. Consequently, even when a very long DRX cycle isconfigured, the transmission timing correction information (TA) istransmitted from the eNB 110, so that the shift of the synchronizationbetween the UE 10 and the eNB 110 is suppressed.

According to the first embodiment, in the case where the DRX cycle isconfigured, the UE 10 transmits the timing adjustment request uplinksignal through the uplink control channel. Consequently, thetransmission timing correction information (TA) is transmitted from theeNB 110, so that the shift of the synchronization between the UE 10 andthe eNB 110 is suppressed without releasing the DRX cycle.

According to the first embodiment, the maximum TA reception interval isdecided based on the movement speed of the UE 10. Thus, the probabilityof the determination may be reduced that the shift of thesynchronization between the UE 10 and the eNB 110 is caused.

According to the first embodiment, when the movement speed of the UE 10exceeds a predetermined threshold value, the UE 10 transmits the timingadjustment request uplink signal to the eNB 110. In other words, onlywhen there is a possibility to occur the shift of the reception timingof the uplink signal at the eNB 110, the UE 10 transmits the timingadjustment request uplink signal. Consequently, it is possible tosuppress the waste of a radio resource due to the transmission of thetiming adjustment request uplink signal.

[First Modification]

Hereafter, a first modification of the first embodiment is explained.Hereinafter, a difference relative to the first embodiment will bemainly described.

According to the first modification, a description will be provided forthe case where a process of adjusting the transmission timing of anuplink signal is essential in the eNB 110, and an extended DRX cycle isset led by the eNB 110.

In such a case, (1-1) when there is one type of extended DRX cycle, ifan adjustment cycle (that is, a maximum TA reception interval in whichtransmission timing correction information (TA) is to be received) toadjust the transmission timing of the uplink signal is longer than theextended DRX cycle, the eNB 110 is configured to permit the setting ofthe extended DRX cycle. Alternatively, when an interval corresponding ton times (n is a real number of 1 or more) as long as the maximum TAreception interval is longer than the extended DRX cycle, the eNB 110may also be configured to permit the setting of the extended DRX cycle.

In addition, the reception interval of the transmission timingcorrection information (TA) is monitored by a predetermined timer(TimingAlignmentTimer), and if the transmission timing correctioninformation (TA) is received, the maximum TA reception interval is setto the predetermined timer. Thus, when the timer with the set maximum TAreception interval has expired, it is determined that the shift of thesynchronization between the UE 10 and the eNB 110 may be caused.

Alternatively, (1-2) when there are a plurality of types of extended DRXcycles, if the maximum TA reception interval is longer than a cycle (theextended DRX cycle) requested from the UE 10, the eNB 110 is configuredto permit the setting of the extended DRX cycle. Alternatively, when aninterval corresponding to n times (n is a real number of 1 or more) aslong as the maximum TA reception interval is longer than the cycle (theextended DRX cycle) requested from the UE 10, the eNB 110 may also beconfigured to permit the setting of the extended DRX cycle.

Based on the above fact, before the predetermined timer (theTimingAlignmentTimer) is expired, the UE 10 transmits the uplink signal.The uplink signal may be autonomously transmitted by the UE 10, or maybe transmitted by the UE 10 according to an instruction of the eNB 110.

(Mobile Communication Method)

Hereinafter, a mobile communication method in the first modificationwill be described. FIG. 9 is a sequence diagram illustrating the mobilecommunication method according to the first modification.

As illustrated in FIG. 9, in step 10, the UE 10 transmits a connectionrequest (RRC connection request) to the eNB 110.

In step 20, the eNB 110 transmits a connection setup (RRC ConnectionSetup) to the UE 10.

In step 30, the UE 10 transmits a connection complete (RRC ConnectionComplete) to the eNB 110.

In step 140, the eNB 110 decides a maximum TA reception interval (TAT inFIG. 9). For example, the maximum TA reception interval is decided basedon the movement speed of the UE 10.

In step 150, the eNB 110 transmits the maximum TA reception interval(the TAT in FIG. 9) decided in step 140 to the UE 10.

In step 160, the UE 10 transmits an extended DRX request for requestingthe setting of an extended DRX cycle to the eNB 110. In addition, whenthere are a plurality of types of extended DRX cycles, the UE 10 mayallow the cycle of the extended DRX cycle selected by the UE 10 to beincluded in the extended DRX request.

In step 170, the eNB 110 determines whether to permit the setting of theextended DRX cycle. Specifically, the eNB 110 determines whether themaximum TA reception interval (or an interval corresponding to n times(n is a real number of 1 or more) as long as the maximum TA receptioninterval) is longer than the extended DRX cycle. When the eNB 110permits the setting of the extended DRX cycle, the eNB 110 proceeds tothe process of step 180. Meanwhile, when the eNB 110 refuses the settingof the extended DRX cycle, the eNB 110 performs the process of step 190and completes a series of processes.

In step 180, the eNB 110 transmits extended DRX permission forpermitting the setting of the extended DRX cycle to the UE 10.

In step 190, the eNB 110 transmits extended DRX refusal for refusing thesetting of the extended DRX cycle to the UE 10.

In step 200, the UE 10 determines whether the setting of the extendedDRX cycle has been permitted. When the setting of the extended DRX cyclehas been permitted, the UE 10 proceeds to the process of step 210. Whenthe setting of the extended DRX cycle is refused, the UE 10 completes aseries of processes.

In step 210, the UE 10 configures the extended DRX cycle.

In step 220, the eNB 110 transmits an uplink signal request forrequesting an uplink signal to the UE 10. For example, the uplink signalrequest is transmitted through PUCCH.

In step 230, the UE 10 transmits the uplink signal, which has beenrequested by the eNB 110, to the eNB 110.

In step 240, the eNB 110 decides transmission timing correctioninformation (TA) between the UE 10 and the eNB 110, according to thereception timing of the uplink signal.

In step 250, the eNB 110 transmits the transmission timing correctioninformation (TA) decided in step 240 to the UE 10. In addition, sincethe DRX is configured, it is preferable that the eNB 110 transmits thetransmission timing correction information (TA) in the On duration.

In addition, the UE 10 adjusts the transmission timing of the uplinksignal based on the transmission timing correction information (TA)received from the eNB 110.

[Second Modification]

Hereinafter, a second modification of the first embodiment will bedescribed. Hereinafter, a difference relative to the first embodimentwill be mainly described.

According to the second modification, a description will be provided forthe case where a process of adjusting the transmission timing of anuplink signal is not essential in the eNB 110, and an extended DRX cycleis set led by the UE 10.

In such a case, (2-1) when there is one type of extended DRX cycle, ifan adjustment cycle (that is, a maximum TA reception interval in whichtransmission timing correction information (TA) is to be received) toadjust the transmission timing of the uplink signal is longer than theextended DRX cycle, the UE 10 requests the eNB 110 to set the extendedDRX cycle. Alternatively, when an interval corresponding to n times (nis a real number of 1 or more) as long as the maximum TA receptioninterval is longer than the extended DRX cycle, the UE 10 may also beconfigured to request the eNB 110 to set the extended DRX cycle.

Alternatively, (2-1) when there are a plurality of types of extended DRXcycles, if the maximum TA reception interval is longer than the extendedDRX cycle selected by the UE 10, the UE 10 requests the eNB 110 to setthe extended DRX cycle. Alternatively, when an interval corresponding ton times (n is a real number of 1 or more) as long as the maximum TAreception interval is longer than the extended DRX cycle selected by theUE 10, the UE 10 may also be configured to request the eNB 110 to setthe extended DRX cycle.

Based on the above fact, before a predetermined timer(TimingAlignmentTimer) is expired, the UE 10 transmits a timingadjustment request uplink signal. The timing adjustment request uplinksignal may be autonomously transmitted by the UE 10, or may betransmitted by the UE 10 according to an instruction of the eNB 110.

(Mobile Communication Method)

Hereinafter, the mobile communication method in the second modificationwill be described. FIG. 10 is a sequence diagram illustrating the mobilecommunication method according to the second modification.

As illustrated in FIG. 10, in step 10, the UE 10 transmits a connectionrequest (RRC Connection Request) to the eNB 110.

In step 20, the eNB 110 transmits a connection setup (RRC ConnectionSetup) to the UE 10.

In step 30, the UE 10 transmits a connection complete (RRC ConnectionComplete) to the eNB 110.

In step 340, the eNB 110 decides a maximum TA reception interval (TAT inFIG. 9). For example, the maximum TA reception interval is decided basedon the movement speed of the UE 10.

In step 350, the eNB 110 transmits the maximum TA reception interval(the TAT in FIG. 10) decided in step 140 to the UE 10.

In step 360, the UE 10 determines whether to request the setting of theextended DRX cycle. Specifically, the UE 10 determines whether themaximum TA reception interval (or an interval corresponding to n times(n is a real number of 1 or more) as long as the maximum TA receptioninterval) is longer than the extended DRX cycle. When requesting thesetting of the extended DRX cycle, the UE 10 proceeds to the process ofstep 360. Meanwhile, when not requesting the setting of the extended DRXcycle, the eNB 110 completes a series of processes.

In step 370, the UE 10 transmits an extended DRX request for requestingthe setting of the extended DRX cycle to the eNB 110. In addition, whenthere are a plurality of types of extended DRX cycles, the UE 10 mayallow the cycle of the extended DRX cycle selected by the UE 10 to beincluded in the extended DRX request.

In step 380, the eNB 110 transmits extended DRX permission forpermitting the setting of the extended DRX cycle to the UE 10.

In step 390, the UE 10 configures the extended DRX cycle.

In step 400, even when a radio resource of an uplink data channel (forexample, PUSCH) has not been assigned, the UE 10 transmits a timingadjustment request uplink signal to the eNB 110 through an uplinkcontrol channel (for example, PUCCH).

In step 410, the eNB 110 decides transmission timing correctioninformation (TA) between the UE 10 and the eNB 110, according to thereception timing of the timing adjustment request uplink signal.

In step 250, the eNB 110 transmits the transmission timing correctioninformation (TA) decided in step 240 to the UE 10. In addition, sincethe DRX is configured, it is preferable that the eNB 110 transmits thetransmission timing correction information (TA) in the On duration.

In addition, the UE 10 adjusts the transmission timing of the uplinksignal based on the transmission timing correction information (TA)received from the eNB 110.

Other Embodiments

The present invention is explained through the above embodiment, but itmust not be understood that this invention is limited by the statementsand the drawings constituting a part of this disclosure. From thisdisclosure, a variety of alternate embodiments, examples, and applicabletechniques will become apparent to one skilled in the art.

Though particularly not mentioned in the embodiment, a configuration fortransmitting the timing adjustment request uplink signal is transmittedfrom the eNB 110 to the UE 10 before a DRX cycle is configured. Theconfiguration for transmitting the timing adjustment request uplinksignal, for example, includes conditions (for example, a predeterminedthreshold value to be compared with a movement speed) for transmittingthe timing adjustment request uplink signal and a transmission cycle fortransmitting the timing adjustment request uplink signal. Theconfiguration for transmitting the timing adjustment request uplinksignal, for example, may be notified to the UE 10 through RRC signaling,or may be notified to the UE 10 through a broadcast channel. Thebroadcast channel is broadcasted from the eNB 110 and transfers MIB(Master Information Block) or SIB (System Information Block).

According to an example, when a DRX cycle (specifically, an extended DRXcycle) is configured, there is considered a case where a setting requestof the DRX cycle is transmitted from the UE 10 to the eNB 110 andsetting permission of the DRX cycle is transmitted from the eNB 110 tothe UE 10. In such a case, it is considered that a configuration fortransmitting the timing adjustment request uplink signal is included inthe setting permission transmitted from the eNB 110 to the UE 10.

Particularly not mentioned in the embodiment, the transmission timing ofthe timing adjustment request uplink signal may be decided according toa maximum TA reception interval and an extended DRX cycle. That is, thetransmission timing of the timing adjustment request uplink signal isdecided such that transmission timing correction information (TA) can bereceived from the eNB 110 in an On duration. For example, thetransmission timing of the timing adjustment request uplink signal isearlier than the start timing of the On duration by a predeterminedtime. The transmission timing of the timing adjustment request uplinksignal may be decided by the eNB 110 or the UE 10.

Particularly not mentioned in the embodiment, when release conditionsfor releasing the extended DRX cycle are satisfied, the extended DRXcycle may be released. In addition, for the release of the extended DRXcycle, the eNB 110 may instruct the UE 10 to release the extended DRXcycle, or the UE 10 may request the eNB 110 to release the extended DRXcycle.

The release condition is that the movement speed of the UE 10 isincreased such that the maximum TA reception interval is notappropriate, that is, the movement speed of the UE 10 exceeds apredetermined threshold value determined by the maximum TA receptioninterval. Alternatively the release condition is that it is not possibleto set the maximum TA reception interval, in which the extended DRXcycle is configurable, as a value of a predetermined timer(TimingAlignmentTimer). Alternatively the release condition is that theeNB 110 determines that the transmission timing of an uplink signal isout of a predetermined range. Alternatively the release condition isthat a variation amount in TA continuously received in the UE 10 fromthe eNB 110 is larger than a predetermined threshold value.

What is claimed is:
 1. A mobile communication method, which configures aDRX cycle having an On duration in which a downlink signal transmittedfrom a serving base station is to be monitored and an Off duration otherthan the On duration in an RRC connected state where an RRC connectionis established between a radio terminal and a radio base station, themobile communication method comprising: a step A of transmitting, fromthe radio terminal to the radio base station, a timing adjustmentrequest uplink signal through an uplink control channel, even when aradio resource of an uplink data channel has not been assigned in a casewhere the DRX cycle is configured; and a step B of transmitting, fromthe radio base station to the radio terminal, transmission timingcorrection information of an uplink signal, in response to the timingadjustment request uplink signal.
 2. The mobile communication methodaccording to claim 1, wherein the step A comprises: a step oftransmitting, from the radio terminal to the radio base station, thetiming adjustment request uplink signal, when a movement speed of theradio terminal exceeds a predetermined threshold value.
 3. The mobilecommunication method according to claim 1, comprising: a step C ofdeciding, at the radio base station, a maximum reception interval, inwhich the transmission timing correction information is to be received,based on a movement speed of the radio terminal; and a step D oftransmitting, from the radio base station to the radio terminal, themaximum reception interval.
 4. The mobile communication method accordingto claim 3, wherein the step A comprises: a step of transmitting, fromthe radio terminal to the radio base station, the timing adjustmentrequest uplink signal, before a reception interval of the transmissiontiming correction information exceeds the maximum reception interval. 5.A radio terminal configured to receive a downlink signal in a mobilecommunication system, which configures a DRX cycle having an On durationin which the downlink signal transmitted from a serving base station isto be monitored and an Off duration other than the On duration in an RRCconnected state where an RRC connection is established between the radioterminal and a radio base station, the radio terminal comprising: acontrol unit configured to transmit a timing adjustment request uplinksignal to the radio base station through an uplink control channel, evenwhen a radio resource of an uplink data channel has not been assigned ina case where the DRX cycle is configured.